Head YOUTEK IG Speed 18x20 is the updated model of Head youtek speed 18 x20 and the new one will more stable.
But if you are a beginner, I suggest you not to choose these 2 racquet since these racquets are designed for advance player which request the player have long and fast swing and higher skill.
Babolat AeroPro Drive GT is a good racquet with solid feel and easy to generate spin, it may fit for you. You also take a look for the following racquets : Head YOUTEK IG Extreme MP, Babolat Pure Drive, Dunlop Biomimetic 300....
At the end, I suggest you to borrow some racquets to try first or ask your coach if you are learning tennis to find a racquet to fit your playing style and skill level.